For obtaining the exact and reliable data during the geodetic works the device under the name a level is used. First of all, before starting the measurements, you should check the level for serviceability, and then make its correct setting. Usually this work is carried out in special geodetic laboratories and covers a number of important operations and procedures that reveal the real parameters of the level and allow you to compare them with the passport data of the device. If these data do not match, then the equipment is considered faulty.
Level (a) and its optical scheme (b): 1, 4, 5, 9, 10 - screws, 2 - stand, 3, 7 - levels, 6 - visual uruba, 8 - reticle, 11 - mounting pressure plate, 12 - objective lens, 13 - focusing lens, 14 - reticle, 15 - eyepiece, 16–19, 21 - prisms and lenses, 20 - mirror, 22 - level.
Checking the level is made in the time specified in its documentation, and if it has expired, then use such a device is not recommended. Such geodetic equipment may be subject to unscheduled inspections for various reasons, for example, due to the loss of the certificate of the level. The method of testing in the laboratory of each instrument depends on its type. Consider the existing types of such equipment:
- optical levels;
- digital devices for determining the difference in height on the ground;
- laser equipment for this work.
The optical scheme of a level with the compensator.
Setting the last type of leveling is the most difficult, and therefore you can’t do it yourself. These laser models are tested by experienced specialists in state-of-the-art laboratories. The verification of such a level includes the general control of individual components of the equipment, setting the required levels, checking the correctness of the compensator suspension, working with the radiation axis and setting the correctness of the horizontal plane of the device, measuring the quadratic error.
Digital level meters without special equipment can not be fine tuned, so they should be checked in special conditions. Such equipment is checked for the accuracy of the installation of the slats (round), the capacity of the digital part (consists of several stages), the range of the compensation system, the presence of systematic and quadratic errors.
Optical level, you can try to customize yourself, if you precisely follow the recommendations of experts.
How to check the optical level?
Setup begins with an external inspection of the device and includes the following conditions:
The device of the laser level: 1 - laser tube, 2 - light guide, 3 - tripod, 4 - transitional part, 5 - lens, 6 - level, 7 - power supply.
- on the body of the level there should be no signs of corrosion;
- there should be no visible mechanical damage;
- all adjustment mechanisms should have a smooth ride, without jerks and delays.
A further method of testing and adjustment depends on the model of the level, but there are general procedures for all types of such optical devices:
- level adjustment;
- identification of symmetry settings and their control;
- the displacement of different axes of the device and finding the angle of displacement between them;
- correct installation of the grid of the telescope of the level;
- quadratic error of the instrument scale divisions.
Initial stage of work
Check begins with an assessment of an external condition and completeness of a level. Then the following parameters are visually examined:
- the purity of the optical surfaces of the optic tube;
- simultaneous image of grid lines should be clear and sharp;
- the ends of the contact level bubble are checked;
- on the level there should be no traces of corrosion and mechanical defects that may interfere with accurate measurements;
- the completeness of the equipment must comply with what is indicated in his passport or certificate.
After that, it is necessary to assess the performance of the level and make sure that the correct interaction of its moving parts. The test is performed on the following parameters:
Types of laser levels.
- serviceability of all parts of the device;
- in the lifting, securing and suggestive cogs should not be detected their swing;
- eyepiece should rotate smoothly, without jerks;
- lifting screws must meet the same requirements;
- mirror level lighting should be checked for the absence of turbidity;
- mounts of moving parts must not be damaged;
- clamping screws for clamping accuracy are examined;
- it is necessary to make sure that the compensator and damper are working, while all the adjustment screws must be set to the middle position;
- examines the condition of the tripod;
- it is necessary to make sure that the screw is suitable for this model of the level.
After that, all the clamping parts on the stand are tightened and checked for stability. To do this, the device is installed on a tripod and actuated: aim the telescope at the rail and produce a readout. Then press (carefully) on the top of the tripod and again take the readings. If the results obtained coincide or differ slightly, and the bubble does not change its position, then the tripod is stable. If not, then you need to find the reason or replace the tripod with a new one.Back to table of contents
Round level check and adjustment
The device of the leveling rod: a - crutch, b - shoe, в - readings on the rail.
To self-tune the optical level you need to start by checking the round level. It represents the normal at the point of the so-called zero-point to the grinding surface. The main condition here is that its axis should be parallel to the axis of rotation of the device.
To check, you need to install the telescope in parallel with any 2 lifting screws, with their help you should try to move the bubble of the circular level to zero-point, and then turn the upper part of the level 180 degrees around the vertical axis.
If, after this action, the vial remains in the center of the capsule, it is possible to consider this verification item completed. If this does not happen, then it is necessary to make an adjustment - perform a number of installations to obtain the desired relative position of the instrument parts and their normal interaction. To do this, using screws to adjust the circular level, it is necessary to shift the vial by ½ deviation to the center of the capsule. Residual inaccuracy is eliminated with the help of so-called lifting screws. These actions are carried out several times until the desired result is obtained.Back to table of contents
Horizontal sight axis and its check
Verification of the cylindrical level. Measurements with unequal distances to the rails.
To set it up, the following condition must be fulfilled: the instrument pointing line must be horizontal when the bubble is in the central part of the zero-point. To check the fulfillment of this condition, it is necessary to choose 2 points (C and M), which are separated by 25-35 m. They install rails in them, and the level is fixed on a tripod so that it is in the middle between these points. The device is driven and take a count on the rails, and then calculate the difference between the levels of the points (C and M). As an example, let us assume that the reading of the level on the first reading is equal to 1.378, and on the second - 1.278 meters. Then the excess (PRS) is equal to the difference of these figures - 0.1. Rearrange the tripod with the level as close as possible to point C and take a new readout on the rail. Suppose it is 1.2 m. Then the theoretical figure is: at the first point, C-PRSP = 1.278, and at the second rail, M-1.2 = 0.078 meters. Then take a new reading on M and compare the resulting figure with the theoretical. If this difference is more than three millimeters, then it is necessary to carry out an adjustment.
Cylindrical level and slopes at bubble position: a - side view, 6 - top view, 1 - ampoule, 2 - liquid, 3 - vial, 4 - correction screw, 5 - ampoule slope.
Unscrew the protective cover on the eyepiece using the alignment pin provided in the leveling set, turn the set screw until the actual reading on the horizontal horizontal bar matches the theoretical result (0.078 meters). Then check again.
If you set the level so that the eyepiece of the tube with the horizontal position of the sighting axis was in front of the slats by two or three centimeters, then you can very accurately determine the height of the tool. A black or black plastic or cardboard cap should be attached to the lens. In its center it is necessary to make a hole of two to three millimeters. The main observer looks through it at the rail, and the assistant installs on it a moving part made of transparent material with a black stroke in the middle. At the direction of the observer, it is set so that the mark falls exactly opposite the hole in the lid. After this is done counting on the rail.Back to table of contents
Installation of the grid lines of the optic tube
To do this, at a distance of 10-15 meters from the level, strengthen the plumb line and bring the equipment into working condition. A vertical grid line is aimed at a plumb line, and if one end is deflected at a distance of more than 1 mm (measured with a ruler), the eyepiece mounting screws are unscrewed and removed, freeing access to the grid. Then correct it by turning it to match the image of the plumb line. The eyepiece is put back in place and the screws are tightened. The check is repeated to verify the correctness of the vertical grid setting.
To check its horizontal threads, the device is aimed at a target 12 meters from the tripod, and then slowly moving the telescope in the horizontal plane with a cog pickup. See whether there is a deviation of the thread from the target. If the difference is more than one millimeter, then adjust the grid in the horizontal plane as well as for vertical lines.Back to table of contents
Efficiency of the compensator
And - in - schemes of an arrangement of axes at checking of a level, g - level positions at the third checking.
To make sure that the compensation system works correctly, the following condition must be fulfilled: when the instrument is tilted, the axis of the telescope should be horizontal within the limits of the compensator's action.
To achieve this, a bubble of a circular level is transferred to a zero-point, and the sight line of the level is aimed at a vertically mounted rail. Produce a thorough focusing of the device and take the first reading (for example, C1). After that, 4 positions of a bubble of a circular level are successively obtained by tilting the axis of the level with screws for lifting to the right, left, back and forth. After each position change, a point count is taken (C2, C3, C4, C5). Then calculate the difference between the indications - (C1 - C2, C1 - C3, C1 - C4, C1 - C5). These values must not exceed 1 mm. If this is not the case, then you must carry the level to the workshop, where you will repair or replace the compensator.Back to table of contents
The correctness of the shift of the line of sight when changing the focus of the telescope
The device is aimed at the rail, carefully focused and take the countdown. Then, with the help of a creamer device, the initial focusing is disturbed. Again, carefully correct the focus of the tube and again take a readout on the rail. The difference should not exceed 1 millimeter. If it is larger, then you need to carry the level to the workshop for repairs.Back to table of contents
Determination of errors in measuring elevations
The position of the bubble level at the performance test performance compensator.
It is carried out in several stages on the ground, using the so-called leveling method from the middle. This is done with the help of two rails with a line of sight with a length of up to 90-100 meters. The places of their fastening are strengthened with leveling crutches or pegs, into which the screws with heads in the form of a sphere are screwed. The slats themselves must be installed strictly vertically and should not change their position throughout all measurements.
The device is strengthened in their section at an equal distance from these rails. It is triggered and 10 exceedances are measured between them. This is one series of measurements. In total, it is necessary to conduct 5-6 such stages. At a level change the horizon before each such measuring series.Back to table of contents
The study of the correctness of the cylindrical level
If the model of the device is applied to the level of a cylindrical type on the telescope, then it must meet the following conditions - its axis must be strictly parallel to the line of sight of the pipe. This check should be done in two stages:
- the sheer plane passing through the main axis of the cylindrical level should be parallel to a similar surface passing through the line of sight of the telescope;
- the projection on the vertical plane of the angle between the axis of the level and the pipe should not exceed the limit set in the passport.
The first condition is checked with the help of a lath installed 45-55 meters from the tripod, the lifting screw of which is directed in its direction. Carefully check the horizontal attachment of the device, combine the ends of the bubble level with a screw, and the fixing mechanism get a clear image. Produce a countdown. Then, tilting the axis of the device is achieved by lifting the screws, so that the readings do not change, and fix the position of the ends of the cylindrical level. The same is done when tilting in the opposite direction. If the bubble remains in place in both cases or its ends are displaced in the same direction, the level setting is considered correct. If this is not the case, then the horizontal and vertical screws of the most cylindrical level are adjusted.
The second condition is verified using methods such as:
- leveling in the forward direction;
- the same, but in combination with measurements from the middle;
- application of the method using different shoulders.
With each method, and they are described in the special literature, at least 3 measurements of the angle between the axis of the level and the projection on the vertical plane should be made. Then, the arithmetic average of these measurements is calculated and compared with the passport data. If the resulting figure does not go beyond the permissible limits specified in the document, then the level is set correctly.Back to table of contents
Applied devices and devices
- Spherical head screws.
- Level with the accompanying set.
Self-tuning of the level is possible subject to all recommendations that have been set out above.
But if it failed, then it is best to contact the specialists from the geodesic laboratory.